=Adding Color and Rennet.=[8]—If the cheese is to be colored, from 1 to 2 ounces of liquid cheese color (Annatto dissolved in an alkali) per 1,000 lbs. of milk is now added and thoroughly mixed into the milk which is then set with rennet. Three ounces of a standard rennet extract to 1,000 lbs. of milk is usually sufficient. Enough should be used so that the milk will show beginning coagulation in 10 to 15 minutes and be ready to cut in 30 to 40 minutes. The extract should be diluted with ten times as much water and is then poured into the milk under vigorous stirring so as to be thoroughly distributed and incorporated in the whole mass. Owing to the scarcity of the raw material for rennet extract during the war, pepsin extracted from hogs’ stomachs has been substituted in many factories and is used either in dry form or as a liquid extract instead of rennet extract. With pepsin as the coagulant it is necessary to ripen the milk somewhat further than if rennet is used, in fact to the danger-point where a little more acidity is apt to do harm and produce a dry and crumbly cheese and loss of butter-fat in the whey. Most cheesemakers therefore prefer rennet when they can get it. The rennet having been added, the milk is left undisturbed until a firm curd has been formed. When the curd breaks or splits sharply before the finger pushed slowly through it, it is ready to be “cut.” [Illustration: Curd knives ] =Cutting.=—Two sets of curd knives are used, each consisting of a metal frame in which tinned steel blades are hung, in one vertically and in the other horizontally. The vertical knife is first carried slowly through the curd lengthwise and crosswise; the horizontal set of blades is then moved carefully through the length of the vat. When the cutting is over, the entire mass should be in cubes about half an inch square. The whey that begins to separate out should be clear and yellow. Milky whey is a sign that the butter-fat is escaping in it; the curd has been broken up too violently. In curdling, the casein encases the butter-fat and the object of the breaking up of the curd in the vat is to expel the whey but retain the fat in the cheese. =“Cooking” the Curd.=—Gentle heat is now applied to raise the temperature gradually to 98° or 100° in the course of about 30 minutes. Meanwhile the small pieces of curd are kept floating in the whey by gentle stirring with a rake and the hands, and are not allowed to pack at the bottom of the vat. The heating is easily regulated by opening the steam valve little by little. Through the “cooking” the pieces of curd shrink to some extent and are hardened so that they will gradually stand livelier stirring without losing butter-fat. After the cooking the curd is left for an hour or so in the whey for a slight acidity to develop and it is then shoved toward the sides of the vat and the whey is drained off. Here again the “Acid Test” may assist in determining when the whey should be drawn.